Refactor xlsx writer

[ccrims0n]

Fix #1911

• Move the writer part to the end of the save()

This is:

- [x] a bugfix
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

[ccrims0n]

@MarkBaker Can someone help with reviewing this PR

[oleibman]

Can you please make a minor change to your test? Rather than editing your test file in place, copy it to the temporary directory (file_get_contents followed by file_put_contents should suffice), run your test against the temporary copy, and delete the temporary copy at the end. The difference between this and your existing test is that, if something goes wrong, we don't lose the good copy of the test file.

[ccrims0n]

@oleibman perfect. will make the changes.

Edit: This is done

[oleibman]

Please unlink the temporary file at the end of your test, and I think this will be good to go.
@MarkBaker and @PowerKiKi , after this last change is made, I would like to proceed with merging this change. Since it will be my first time doing that (I am reviewing one other), I just want you to alert you about that in case something goes amiss.

[PowerKiKi]

in case something goes amiss

As long as GitHub is all green, merging should be fine. But I'll keep an eye open...